Are blacklights hazardous?

My roommate and I have set up a couple fairly strong black lights in our dorm room. They're forty watt fluorescent tubes about three feet tall, and look quite cool.

However, we are both wondering whether there's any health risk associated with being exposed to the black lights for an extended period of time. They're the sort of light you purchase at a novelty store like Spencer's Gifts. I would expect that nothing sold under those circumstances would emit any significant radiation at potentially harmful wavelengths, but perhaps I'm too trusting.

Blacklight like ones you see over in clubs are UVA. Those arent as dangerous as germicidal light - UVC. My UVC light burned down plants in a few hours. I wont recommend sitting under blacklight for extended periods of time though.. you may get a malignant melanoma so why risk it?

"It all depends on the dose and wavelength of the radiation. UVA (315 - 400 nm) is pretty harmles. This is what you get from those black-light disco tubes. It is not dangerous if you don't stare to the tubes for long periods. The dose remains so low that you don't even get suntan."

There is some additional radiation at 185 nm, but this is lower in magnitude and off the peak of the weighting curve.

The limit at that freqency is 60 joules/meter^2 in an 8 hour period, which really isn't a lot. A 40 watt UV bulb would generate 40 joules/second at 100% efficiency. Without a meter, I guess you could (over)-estimate the radiation flux by assuming 100% efficiency on the part of the UV bulb, and divide the power (joules/sec) by the total area of the walls and ceiling (in m^2) to get (joules/m^2) / sec.

If we had 100m^2 of area that would reach the above limit in a couple of minutes, unless I'm making a major calculational error (?!).